1. Field of the Invention
The present invention provides a light source system and a display apparatus comprising the same, and particularly, relates to a light emitting diode (LED) light source system with high luminance and a display apparatus comprising the same.
2. Descriptions of the Related Art
Currently, more projection display apparatuses are adopting light emitting diodes (LEDs) as the light source in an attempt to increase the color gamut and decrease the power consumption. Because its short startup time and long life, light source of LED is used to replace high-pressure-mercury lamps in conventional projection display apparatuses. However, as a kind of divergent light source, LED is restricted by the étendue conservation law that makes the light source effective only within a limited light source area and a limited angle. Consequently, the luminance of the projection display apparatus cannot be improved by simply adding more LED light sources. As a result, it is important to improve the luminance of a projection display apparatus adopting LEDs as the light source.
A light source module employing LEDs as the light source and a projection system comprising the light source module are disclosed in U.S. patent application Ser. No. 11/081,825. The light source module, a structure of which is depicted in FIG. 1A, drives the LEDs with discrete pulses and provides increased luminance by receiving a high current input. As shown in FIG. 1A, such a light source module 1 comprises a first LED 111, a second LED 112, a mirror wheel 12, and a power control device (not shown). The two LEDs 111, 112, with the mirror wheel 12 disposed therebetween, are disposed such that their light emitting paths are substantially orthogonal to each other.
As depicted in FIG. 1B, the mirror wheel 12 rotating about its axis 123 comprises a plurality of interleaved reflective segments 121 and transmitting segments 122. When the power control device supplies a current to the first LED 111 to emit light, one transmitting segment 122 of the mirror wheel 12 will be rotated synchronously to a position corresponding to a direction in which the first LED 111 emits light, so that the light can transmit therethrough and exit towards the output direction. On the other hand, when the power control device supplies a current to the second LED 112 instead and switches off the current input of the first LED 111, one reflective segment 121 of the mirror wheel 12 will be rotated to a position corresponding to a direction in which the second LED 112 emits light, so that the light from the second LED 112 is reflected and propagates in the same output direction. In this way, the two LEDs as a whole can provide the desired light beams in a fast alternating manner, resulting in an almost continuous light as perceived by the human eye.
FIG. 2 is a schematic graph depicting the alternating emission duty cycle of the aforesaid light emitting structure. More specifically, the alternating emission of the two LEDs will result in a higher luminance, as well as a light flux of an On-State (i.e., the “flat peak section” labeled by symbol A) in the output light, which is adapted to form a nearly continuous light flux along the time axis as a replacement for the continuous operation mode of a single LED.
However, in the practical operation of this structure, since the mirror wheel 12 consists of a plurality of reflective segments 121 and transmitting segments 122 interleaved with each other, a number of border regions will be inevitably formed therebetween. If a light beam from either of the LEDs impinges entirely or partially on such border regions, not only will light be lost, but also the instantaneous output light flux will be degraded.
To avoid the aforesaid light loss, the LEDs must be controlled to not emit light in the border regions as far as possible. However, since positions for two LEDs already have fixed, the only solution is to switch off the operating LED in advance when the border region of the mirror wheel 12 is nearly approaching a light beam of a LED, after which the opposite LED will be switched on immediately. In other words, the border regions should be accompanied with an Off-State (i.e., the “narrow trough section” labeled by symbol B) as fast as possible. The opposite LED will be allowed to emit light only when the border region passes by the LED.
However, as is well known, LEDs provide a highly divergent light beam, rather than a collecting light beam from an ellipsoidal lamp or a parallel light beam from a parabola lamp. As a result, the light beam projected on by an LED will actually occupy a substantial area on the mirror wheel 12, which makes it impractical to switch the LEDs on and off in advance to achieve a desired effect. In addition, when border regions are skipped, the borders regions on the mirror wheel 12 will create a substantial unusable area on the mirror wheel 12. This will not only undoubtedly shorten the desirable “flat peak sections” and lengthen the unwanted “narrow trough sections” in the otherwise continuous light flux, but also exacerbate the discontinuity in the light flux and degrade the usage efficiency of the mirror wheel 12 significantly. Furthermore, this structure relies entirely on a mirror wheel to integrate the light beams. Each additional mirror wheel may further increase the size of the projection display apparatus significantly. Therefore, in consideration of practical requirements on size of a projection display apparatus, luminance improvement this structure may provide is limited.
In summary, the LED light source structure used in the prior art projection display apparatuses has deficiencies, such as low light emission efficiency, limited room for the improvement of luminance and discontinuous light flux. In view of this, it is highly desirable to provide a light source system with higher luminance, continuous light flux and increased light emission efficiency.